BACKGROUND: Dyssynchronous left ventricular (LV) contraction due to permanent right ventricular apex (RVA) pacing or delayed electrical activation as typically observed in left bundle brunch block (LBBB) has a negative impact on LV function. Objective was to evaluate the impact of epicardial single-site LV pacing in children on LV function and resynchronization. PATIENTS: Single-site epicardial LV free wall pacing was established in 6 children with congenital heart disease and echocardiographic signs of LV dyssynchrony. Reasons for dyssynchrony were either long-term RVA pacing (n=5; pacing duration: 7.7+/-2.4 years) or LBBB with drug-resistant congestive heart failure (n=1). RESULTS: After 1 month of single-site LV pacing, LV ejection fraction increased (41+/-6 versus 53+/-8%) and LV enddiastolic volume decreased (70+/-22 versus 63+/-18 ml/m(2)) as compared to pre-implant measurements. Interventricular mechanical delay decreased (67+/-15 versus 16+/-15 ms) and intraventricular synchrony was restored (septal-to-posterior wall motion delay: 312+/-24 versus 95+/-57 ms). Accordingly, circumferential 2D strain demonstrated a decrease of LV mechanical delay (201+/-35 versus 99+/-23 ms). CONCLUSION: After 1 month of single-site LV pacing, conventional and 2D strain derived echocardiographic measurements indicated improved ventricular function and synchronization in children with previous RVA pacing or LBBB. Further studies are needed to evaluate whether single-site LV pacing may be sufficient for resynchronization therapy.